An implantable medical lead of an implantable medical system carries electrical stimulation signals from a pulse generator located at an implantation site of a patient to one or more electrodes at a distal end of the implantable medical lead that are located at a stimulation site of the patient. Electrical conductors within an insulative body of the implantable medical lead provide a conduction path for the electrical stimulation signals to traverse.
Patients having implantable medical systems that include implantable medical leads may have the need to undergo MRI scans. During the MRI scan, the patient is exposed to a relatively large static magnetic field of 1.5 Tesla or more as well as a smaller gradient magnetic field. While the magnetic fields may have a specific and known orientation relative to the scanning bore of the MRI machine and therefore to the body of the patient, it is noteworthy that the implantable medical lead and particularly the distal end within the patient may have any number of orientations relative to the magnetic fields.
Within the MRI, the patient is also exposed to a relatively high power radio frequency (RF) electromagnetic energy in the megahertz frequency range. This RF electromagnetic energy presents a potentially dangerous situation for the patient during the MRI scan. The RF electromagnetic energy may couple to the conductors within the implantable medical lead that provide the conduction path to the electrodes and thereby create relatively high levels of RF electrical current that produces heating of the tissue surrounding the electrodes. This is especially problematic for implantable neurostimulation systems where the electrodes are positioned in highly vulnerable stimulation sites such as within the brain or adjacent to the spinal cord.